1. Field of the Invention
The present invention relates to a vehicular engine cooling apparatus used in a vehicle, such as an automobile, and adapted to cool an engine and/or its environment after the engine is stopped.
2. Description of the Related Art
When an engine is stopped immediately after a vehicle, such as an automobile, goes up a steep slope or continuously runs at high speed on a superhighway, the temperature in an engine compartment rises due to a shortage of cooling air, and vapor lock occurs in a fuel injection valve, fuel supply passage, etc., possibly making the engine operation unstable at the restart of the engine. In order to prevent the vapor lock, the electrically-operated cooling fan may be operated to lower the temperature of the engine and its environment to a level where that the vapor lock is not liable to occur, after the engine is stopped.
If the cooling fan is operated without any restriction after the engine is stopped, however, a battery for use as its power source is wasted, and undue motor noises are produced. In a conventional engine cooling apparatus, therefore, the environmental temperatures of the engine, such as the fuel temperature, are monitored after the engine is stopped, and the engine and its environment are cooled by the cooling fan for a predetermined time when the monitored temperatures are higher than a preset temperature. In a gasoline engine car, the cooling apparatus of this type can produce a measure of effect against vapor lock.
In an automobile, e.g., an alcohol engine car, which uses a mixed fuel, however, if a mixture of gasoline and methanol is used for an alcohol fuel, for example, a so-called azeotropic effect is produced such that the saturated vapor pressure of the fuel becomes much higher than that in the case where pure gasoline or pure methanol is used for the fuel, provided that the methanol mixture ratio, that is, the mixture ratio of methanol to gasoline, is within a specific range. This azeotropic effect is not limited to the case of the mixture of gasoline and methanol, and may be generally observed when a mixture of two or more different fuels is used for the fuel. In a vehicle which uses two or more different fuels for its working fuels, therefore, vapor lock can very easily occur, so that the engine cannot be readily restarted.